1. Field of the Invention
The present invention relates to a cathode catalyst for fuel cells. More specifically, it relates to a cathode catalyst for fuel cells which contains an alloy of platinum, iron and the third component including one or more sorts of elements selected from the group consisting of tungsten, titanium, molybdenum, rhenium, zinc, manganese, tin, tantalum and rhodium.
2. Description of the Related Art
As for a catalyst used for the cathode of fuel cells, platinum has been conventionally used. In this case, it is known that, by alloying platinum and iron and using thereof for a cathode catalyst, the activity of oxygen reduction will be increased, so the batteries can become high output.
For instance, Japanese Unexamined Patent Publication (KOKAI) No. 60-7941 discloses an electrode catalyst containing a super-lattice structure platinum-iron alloy dispersed on the supports.
However, in a case where the acid electrolyte which consists of a high polymer material having SO3H group, such as a perfluorocarbon acid ionomer, is used as the electrolyte of a fuel cell and the cathode catalyst of a fuel cell is made to contain a platinum-iron alloy, it may arise that the iron contained in a platinum-iron alloy elutes into the electrolyte of a fuel cell. That is, the electrolyte will become strong acid when having SO3H group and swelled with water. In such a case, if the cathode catalyst of a fuel cell is made to contain a platinum-iron alloy, a base metal like iron will be eluted out as ions. The eluting ions are ion-exchanged with the proton in the electrolyte, i.e., H+ of SO3H group. This leads to deterioration of the conductivity of the high polymer electrolyte. As a result, it will arise the problem that the battery performance will be lowered and the life span of a fuel cell is unable to be extended.